The subject matter of the present invention is a process for the manufacture of trichlorosilane and/or silicon tetracholoride by reacting metallic, aluminum-containing silicon at 260.degree. to 1200.degree. C. with hydrogen chloride or chlorine and subsequently separating the resulting reaction mixture.
Crude silicon contains up to 2% by weight of aluminum and iron in the form of impurities. In the manufacture of trichlorosilane and silicon tetrachloride from crude silicon and hydrogen chloride, these impurities are converted to aluminum chloride (AlCl.sub.3) and ferrous chloride (FeCl.sub.2). Under normal reaction conditions, unlike the ferrous chloride, all the aluminum chloride emerges from the reaction zone at temperatures above 260.degree. C. in gaseous form owing to its relatively high vapor pressure, and is deposited in the form of a white to yellowish crystal mass on the walls of the separation and condensation system connected to the reaction zone. In the reaction of crude silicon with chlorine, in addition to aluminum chloride, ferric chloride (FeCl.sub.3) is formed which behaves in a corresponding manner. As a result, the insides of the pipes become encrusted and clogged and the cooling devices used become obstructed. Consequently, it is often necessary after a short time for the pipe systems to be opened and freed of the aluminum chloride that has crystallized out onto them. As a result of the fact that trichlorosilane, silicon tetrachloride and aluminum chloride are extremely readily hydrolysable and owing to the combustibility of trichlorosilane and the high-boiling chlorosilanes produced in side reactions, apart for there being general work-hygiene problems, considerable costs are also incurred. In addition it is necessary to use coolers that have a large surface area, or scraper coolers in which the wall deposit which forms is continuously scraped off by means of built-in rotating components. Rinsing out the solid material that has been scraped off and covering the shaft guide means in particular, present problems here, however.